Conventionally, as for the unshaped refractories used in equipment for desiliconizing molten iron, a ladle for steel-making, RH equipment for steel-making and so forth, the following kinds of unshaped refractories have been put in practical use, until today. That is to say, one example in practical use is unshaped refractories made of a line of alumina-spinel, resulting from improving the corrosion-resistance and the slag penetration-resistance that the unshaped refractories made of a line of high alumina-spinel has. (See Published Patent Application No. 55-23004, Published Patent Application No. 59-128271, Published Patent Application No. 64-87577). And, it may be a case, another example in practical use is unshaped refractories made of a line of alumina-magnesia. (See Published Patent Application No. 63-218586).
Generally, it is known that the corrosion-resistance and the slag penetration-resistance of the unshaped refractories are governed by the corrosion-resistance and the slag penetration-resistance of a portion of fine particles. (Note: the portion of the fine particles is equivalent to a matrix of the unshaped refractories. Generally, a matrix means ‘continuous metal phase that includes a number of pores and/or other kinds of particles made of other gradient inside of the structure, to serve as a base in a sintered material’. In this invention, the portion of the fine particles in the formed unshaped refractories is defined as matrix.)
Taking the above-mentioned matter into consideration, fine particles made of spinel (the composition of the spinel is 28.3% MgO—Al2O3) are used for a part of the fine particles, in case that the unshaped refractories made of a line of alumina-spinel are used. They are used to a considerable amount. In comparison with alumina, such spinel has the characteristic of high corrosion-resistance and has an effect on prohibiting slag penetration, while trying to improve the characteristics of the corrosion-resistance and the slag penetration-resistance.
On the other hand, as for unshaped refractory made of a line of alumina-magnesia, fine particles made of alumina and magnesia are used for a part of the fine particles, while trying to improve the characteristics of the corrosion resistance and the slag penetration-resistance, expecting the action of the spinel that generates at high temperature on usage.
(Note: From a general technical viewpoint, ‘spinel’ means aluminate-magnesium (MgO—Al2O3). In this invention, the substance, whose composition is 28.3% MgO—Al2O3, is defined as spinel. Additionally defining, the spinel has a spinel-structure in the phase-diagram of Al2O3—MgO. And the substance having the state of 28.3% MgO—Al2O3 composition is called for the substance having spinel-structure (in other word, spinel-texture). (See FIG. 7, which relates to a general phase-diagram of Al2O3—MgO in the conventional technology.) Supplementary explaining, in this invention, ‘structure’ means the macroscopic relation between the pore and the particle, which have a variety of figures and sizes respectively.
Briefly explaining in a fundamental way, in case of the above-mentioned unshaped refractories made of a line of alumina-spinel, the whole of the fine particles and the ultra fine one, where the particles constitute a matrix, have spinel-composition, so as to try to improve the corresponding corrosion-resistance. However, focusing on such a technology, fine particles and ultra fine one of the spinel cost high. Especially the ultra fine particles require spending the cost to even higher extent, resulting in encountering with such a problem as economical efficiency.
Furthermore, in case of using such unshaped refractories, the ultra fine particles made of alumina, which are added for improving the mobility under construction, react with spinel at high temperature range. In the same way, the alumina cement, which is added as a binder for securing the strength at normal temperature, react with spinel at high temperature range. Consequently, there occurs a tendency for composition of the matrix portion to shift from a spinel-composition to an alumina-rich side. Resultantly, it was pointed out that corrosion-resistance and slag penetration-resistance become relatively inferior, in comparison with the unshaped refractories made of alumina-magnesia. In addition, there is the following attempt to solve such a disadvantage in the world. That is, it may be a case, fine particles made of magnesia are added in order for the composition not to shift to an alumina-rich side.
Taking a look at another one in the above-mentioned unshaped refractories, which means the unshaped refractories made of a line of alumina-magnesia, cubical expansion happens, accompanied by the change of the crystal structure, when the spinel generates in the reaction-procedure in the high temperature region. Resultantly, it may be a case, cracks generate. This invites the anxiety about the inferiority of the structural stability. Furthermore, when the magnesia spreads into the surrounding alumina-phase, a one-way diffusion-phenomenon happens. At such a stage, the trace generates after the fine particles of the magnesia spread, in which the fine particles of the magnesia previously existed. Resultantly, such a trace, where the fine particles of the magnesia previously existed, becomes to be a form of pore. Such pores cause cubical expansion, resulting in degrading the slag penetration-resistance. From the standing point of the corrosion-resistance, both of the above-mentioned two reasons, which are, less structural stability and less slag penetration-resistance bring about a serious problem.
The technical problem caused by the conventional technology mentioned above is shown in FIG. 5. FIG. 5 is related to the conventional technology, showing a conception drawing concerning how alumina-magnesia material as a refractory one changes the structure, associated with the change of sintering-temperature.
Concerning the structure of the sintering-temperature up to approximately 1100° C., a numeric reference No. 51 is fine particles made of magnesia(MgO). No. 52 is mainly alumina and the other mixed substances mutually. In the structure of the sintering-temperature up to approximately 1300° C., a numeric reference No. 53 means a mixture of magnesia (MgO) and the other mixed substances. At such sintering-temperature, the magnesia (MgO) spreads outwardly from the center of the magnesia particles to the outer direction. That is to say, such diffusion is done to spread in one-way direction. In this case, there occurs no mutual diffusion, which means, this diffusion is not done in the opposite way, face to face against arrow-mark (5a) in FIG. 5. Furthermore, when the magnesia (MgO) is sintered to an extent of high temperature, up to approximately 1500° C., the magnesia advances more diffusing in one-way. On such a stage, spinel generates in the portion of a numeric reference No. 53. However, at the same moment, the pore (54) caused by the trace generates. The trace generates by an omission of magnesia (MgO), though. These pores bring about the rate of unrequited high porosity. And these pores do the rate of unrequited thermal expansion in the unshaped refractories. After all, the unshaped refractories end up in having the high rate of permanent linear expansion (permanent linear change on reheating). Here, the high rate is one kind of the defective characteristics as physical properties of unshaped refractories.
Further, the conventional technology is accompanied with the following defective problem. That is, fine particles made of magnesia, which are used as raw materials, react with water to cause hydration-collapse. Such water is added under construction, though. Resultantly, the unshaped refractories receive a damage of such hydration-collapse. (Note: in this invention, ‘hydration-collapse’ means a phenomenon where refractory-structure breaks by expansion, being influenced by the hydration reaction.). Furthermore supplementary explaining, the fine particles made of magnesia have a possibility to enforce the hardening-time of cement to fluctuate when the material is mixed with water.
As mentioned above, in comparison with the unshaped refractories made of aluminum-magnesia, the unshaped refractories made of aluminum-spinel have the following tendency on usage. That is to say, in case of aluminum-spinel, the matrix-structure on usage falls within a range of alumina-rich, resulting in inviting such a problem that the corrosion-resistance and the slag penetration-resistance become inferior. Concerning another one, which is, in case of the unshaped refractories made of aluminum-magnesia, the matrix-structure on usage becomes spinel. Although such spinel gives the unshaped refractories the characteristics of the high corrosion-resistance and the slag penetration-resistance to some degree, the cubic expansion occurs and pores generate, resulting in the serious problems such as cracking and breaking, simultaneously with generating the spinel. It is associated with inferiority in structural stability. Not only the structural stability but also the slag penetration-resistance deteriorates by the reason of generating pores, resulting in much less improvement of the characteristics than the expectation.